"""
Fetch scalar value with timeout
+++++++++++++++++++++++++++++++

Send a SNMP GET request
* with SNMPv2c, community 'public'
* using Twisted framework for network transport
* over IPv4/UDP
* to an Agent at 195.218.195.228:161
* wait 3 seconds for response, retry 5 times (plus one initial attempt)
* for an OID in tuple form

This script performs similar to the following Net-SNMP command:

| $ snmpget -v2c -c public -ObentU -r 5 -t 1 195.218.195.228 1.3.6.1.2.1.1.1.0

"""#
from twisted.internet import reactor, defer
from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413.twisted import cmdgen
from pysnmp.carrier.twisted.dgram import udp

# Create SNMP engine instance
snmpEngine = engine.SnmpEngine()

#
# SNMPv2c setup
#

# SecurityName <-> CommunityName mapping
config.addV1System(snmpEngine, 'my-area', 'public')

# Specify security settings per SecurityName (SNMPv1 - 0, SNMPv2c - 1)
config.addTargetParams(snmpEngine, 'my-creds', 'my-area', 'noAuthNoPriv', 1)

#
# Setup transport endpoint and bind it with security settings yielding
# a target name
#

# UDP/IPv4
config.addTransport(
    snmpEngine,
    udp.domainName,
    udp.UdpTwistedTransport().openClientMode()
)
config.addTargetAddr(
    snmpEngine, 'my-router',
    udp.domainName, ('195.218.195.228', 161),
    'my-creds',
    timeout=300,  # in 1/100 sec
    retryCount=5
)

# Error/response receiver
def cbFun(response, *args):
    snmpEngine, errorIndication, errorStatus, errorIndex, varBinds = response
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print('%s at %s' % (
                errorStatus.prettyPrint(),
                errorIndex and varBinds[int(errorIndex)-1][0] or '?'
            )
        )
    else:
        for oid, val in varBinds:
            print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    reactor.stop()

# Prepare request to be sent yielding Twisted deferred object
df = cmdgen.GetCommandGenerator().sendVarBinds(
    snmpEngine,
    'my-router',
    None, '',  # contextEngineId, contextName
    [ ('1.3.6.1.2.1.1.1.0', None) ],
)

# Register error/response receiver function at deferred
df.addCallback(cbFun)

# Run Twisted main loop
reactor.run()